Multifilar Hemispherical Helical Antennas

Helices are broadband antennas that provide moderate gain, largely real input impedance and circular polarization when operating in the axial mode regime. A modified form of the helix, the spherical helix, has been shown to yield similar polarization and gain characteristics over a narrow bandwidth but a much larger beamwidth. This investigation examines multifilar hemispherical helices and produces two specific designs with some desirable radiation characteristics. The side-fed quadrifilar helix and the top-fed bifilar helix are the new hemispherical designs which are studied in detail both numerically and experimentally. The Numerical Electromagnetics Code 4 is used to analyze the radiation characteristics of the proposed multifilar hemispherical helices. Directivity, E- and H-plane radiation patterns, axial ratio and input impedance of a few example designs are calculated. Measurements, taken in the anechoic chamber at the Virginia Tech antenna range, generally confirmed the simulation results. It is shown that the bifilar hemispherical helix provides a flat gain curve over the measured bandwidth (~14%) and generally elliptical polarization with near circular polarization in limited case.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Electrical and Computer Engineering

Department dc:contributor.department

Electrical and Computer Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2003

Author dc:creator

• Clark, Jeffrey R.

Chair dc:contributor.committeechair

• Safaai-Jazi, Ahmad

Committee members dc:contributor.committeemember

• Davis, William A.
• Besieris, Ioannis M.

• quadrifilar helix
• helical antennas
• multifilar helices
• NEC-4

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

etd-12112003-095406

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/36060